Endothelial cell chemotaxic activity expressed in rat placenta is not associated with prolactin-like proteins B and C

Conditioned medium from gestation day 18 rat placental cultures showed potent stimulation of the directional migration of human retinal endothelial cells. To examine the role of major secreted placental proteins in this chemotaxic activity, prolactin-like proteins (PLPs)-B and C were purified from rat placenta using immuno-affinity chromatography. In contrast to conditioned medium, native PLP-B and PLP-C preparations failed to show any significant stimulation of endothelial cell migration. This study further examined the ability of PLP-B to bind to rat receptors for growth hormone (GH-R) and prolactin (PRL-R). In competitive binding assays with [125I]-hGH, neither native nor recombinant PLP-B preparations showed significant high affinity binding to the transfected rat GH-R or PRL-R. In summary, neither PLP-B nor PLP-C exhibit the potent chemotaxis stimulatory activity of placental conditioned media, nor does PLP-B show evidence of ability to act via rat GH or PRL receptors.